1. Field of the Invention
The invention relates to a short-arc discharge lamp for UV irradiation which, for example, is used in the production of semiconductors and liquid crystals. More particularly, the invention relates to a foil seal arrangement on the cathode side of a large short-arc discharge lamp.
2. Description of Related Art
Among short-arc discharge lamps for semiconductors and liquid crystals, large short-arc discharge lamps with an input electric power of, for example, greater than 1 kW are generally those that use foil sealing to ensure sealing of the discharge space. In short-arc lamps using this foil sealing, it is known that there is a defect in which a gas emerges from the foil sealing areas and destroys the lamps. An explanation for this defect is that the positive ions (i.e., cations) of metallic impurities, and the like, in the quartz glass are attracted by the negative electrical charge on the side of the cathode and in the foil sealing area on the side of the cathode, and that the positive ions concentrated on the cathode side and the foil sealing area detach the metal foil from the quartz tube part surrounding the metal foil. To eliminate this defect, an arrangement of a wire with the same electrical potential, which electrically connects on the outer surface of the quartz tube on the side of the cathode to the cathode, is implemented, as is described in Japanese patent disclosure HEI 4-40828 and its counterpart U.S. Pat. No. 4,673,843, for example, both of which are incorporated herein by reference.
FIG. 6 shows a conventional example of the arrangement of the foil sealing area on the cathode side of a short-arc discharge lamp with an input electrical power of greater than or equal to 1 kW, in which the above described wire with the same electrical potential is located. This lamp consists of the following:
a bulb part 51 which jackets the emission space,
a cathode 52 which is located in this bulb part 51;
an inner lead pin 53 which is connected to the cathode 52;
an inner lead pin holding component 54 which holds the inner lead pin 53 securely;
a metal disk 55 which is connected to the end opposite the side of the cathode 52 of the inner lead pin 53;
a metal foil 56 which is welded to the metal disk 55;
a sealing quartz component 57 which is in contact with the inside of the metal foil 56;
a quartz tube part 58 which is in contact with the outside of the metal foil 56;
an outer lead pin 59;
a metal disk 60 which connects the outer lead pin 59 and the metal foil 56 to one another;
a foil sealing area 61 which ensures the sealing action of the lamp;
a metal base 62;
a line 63;
a terminal part 64 which connects the line 63 to the above described lead pin; and
a wire 65 which provides the same electrical potential between the metal base, which is electrically connected to the cathode 52, and the outer surface of the quartz tube.
For the metal foil 56, which is used for the foil sealing area 61, a strip-like foil with a thickness of a few tenths of a micron is used. The foil is made of a metallic material having a high melting point, such as molybdenum or the like. In the foil sealing area 61, the sealing action of an emission space is ensured by the metal foil 56. The sealing quartz component 57, which is in contact with the inside of the metal foil 56, and the quartz tube part 58, which is in contact with the outside of the metal foil 56, are located directly tightly adjacent to one another. The above-described defect is in the adhesion area, in which the metal foil 56 and the quartz tube part 58 which surrounds the metal foil are located directly tightly adjacent to one another, comes off. Specifically, the defect wherein positive ions of metallic impurities, and the like, in the quartz glass are attracted by the negative electrical charge on the side of the cathode 52 and are concentrated on the foil sealing area 61 on the side of the cathode 52, such that the positive ions concentrated on the foil sealing area 61 detach the metal foil 56 from the quartz tube part 58 that surrounds the metal foil 56, which is prevented by the use of a wire 65 which provides the same electrical potential to the outer surface of the quartz tube on the side of the cathode to the cathode by electrically connecting them, as described above.
According to increased market demand, the size and power rating of short-arc discharge lamps are becoming larger and larger. According to the input electrical power of the lamps of, for example, greater than 4 kW, the diameter and a length of the foil sealing area 61 shown in FIG. 6 are becoming larger and larger. For a lamp of this size, the operating pressure during luminous operation is greater than or equal to 2xc3x97106 Pa, which creates a new problem, i.e., that the foil floats between the metal foil 56 and the sealing quartz component 57 which is in contact with the inside of the metal foil 56.
An object of the invention is, therefore, to prevent the phenomenon of foil floating between the metal foil 56 located in the foil sealing area 61 and the sealing quartz component 57 in contact with the inside of the metal foil 56 in a large lamp with an electrical input power of greater than 4 kW and with an operating pressure during luminous operation of greater than or equal to 2xc3x97106 Pa.
It is another object of the invention to prevent cracks from forming in the foil sealing area 61, the leakage of gas from the lamp, and the premature breaking of the lamp during luminous operation.
Thus, in an embodiment of the present invention, there is provided a short-arc discharge lamp which includes:
electrodes which are located in an emission space;
a metal foil which is electrically connected to the electrodes;
a quartz tube part which surrounds the above described metal foil;
a sealing quartz component which is in contact with the inside of the metal foil;
a metallic component which is inserted into the above described sealing quartz component and which is electrically connected to the metal foil; and
a foil sealing area formed by the metal foil, the quartz tube and the sealing quartz component sealed against one another, and by which a sealing action of the above described emission space is ensured. The short-arc lamp has an electric input power greater of than or equal to 4 kW and an operating pressure during luminous operation of greater than or equal to 2xc3x97106 Pa, and is operated using direct current.
The above-mentioned characteristics of the invention are achieved by the length of the area of the metallic component inserted into the sealing quartz component being greater than or equal to roughly 40% of the total length of the sealing quartz component.
The object characteristics of the lamp of the present invention are furthermore achieved in that at least in one part of the foil sealing area on the cathode side there is an electrically conductive component which is electrically connected to the cathode along the outside surface of the quartz tube part.
Furthermore, it is another object of the invention to provide a short-arc discharge lamp that includes:
electrodes which are located in an emission space;
a metal foil which is electrically connected to the above described electrodes;
a quartz tube part which surrounds the above described metal foil;
a sealing quartz component which is in contact with the inside of the metal foil;
a metallic component which is inserted into the above described sealing quartz component and is electrically connected to the metal foil; and
a foil sealing area formed by which the metal foil, the quartz tube and the sealing quartz component sealed against one another, and by which a sealing action of the above described emission space is ensured. The short-arc lamp has an operating pressure during luminous operation greater than or equal to 2xc3x97106 Pa, and is operated using direct current.
It is an object of the invention that the length of the area of the metallic component inserted into the sealing quartz component is greater than or equal to roughly 40% of the total length of the sealing quartz component, and that the diameter of the metallic component on the cathode side is less than the diameter on the side of the feed point and/or the diameter of the opening of the sealing quartz component for inserting the lead pin on the cathode side is greater than on the insertion opening side for the lead pin.
It is still another object of the invention to provide a short-arc discharge lamp which includes:
electrodes which are located in a emission space;
a metal foil which is electrically connected to the above described electrodes;
a quartz tube part which surrounds the above described metal foil;
a sealing quartz component which is in contact with the inside of the metal foil;
a metallic component which is inserted into the above described sealing quartz component and moreover is electrically connected to the metal foil; and
a foil sealing area formed by the metal foil, the quartz tube and the sealing quartz component being sealed against one another, and by which a sealing action of the above described emission space is ensured.
It is another object of the invention to provide a short-arc lamp that has an operating pressure during luminous operation greater than or equal to 2xc3x97106 Pa, and which is operated using direct current, and further has a metal foil or a metal line is electrically connected to the cathode-side tip of an outer lead pin and that this metal foil or the metal line is inserted from a lead pin insertion opening side of the sealing quartz component as far as a position at which greater than or equal to roughly 40% of the total length is reached.
The invention address the problem defect of the foil floating phenomenon in the foil sealing area in a large lamp with an electric input power greater than or equal to 4 kW which results in the case of an operating pressure during luminous operation of greater than or equal to 2xc3x97106 Pa, in spite of using the above described wire with the same electrical potential.
It has been found that in the case of one such high luminous pressure on the inside surface of the foil of the sealing area the foil floating phenomenon arises. The object of the invention is to suppress the floating phenomenon on the inside surface of the metal foil and the sealing quartz component which is in contact with the inside of the metal foil.
As described, by inserting a metallic component, such as an outer lead pin or the like, as far as a position which comprises greater than or equal to roughly 40% of the total length of the sealing quartz component so as to prevent the concentration of positive ions on the inside surface of the metal foil. If the metallic component is inserted as far as a position which comprises greater than or equal to roughly 40% of the total length of the sealing quartz component, it receives heat from the cathode, by which the temperature of the metallic component rises and as a result of oxidation the volume of the metallic component expands. In this case, if the diameter of the outer lead pin insertion opening of the sealing quartz component is less than the outer lead pin which undergoes a volume expansion due to oxidation, a stress arises as a result of the volumetric expansion. As a result, cracks and the like are formed, which leads to breakage of the lamp. Therefore, there is provided a gap between the metallic component, such as the outer lead pin or the like, and the sealing quartz component and the gap absorbs the above described volumetric expansion to an adequate degree.
FIG. 5 shows the degree of formation of the foil floating phenomenon in the case of a high luminous pressure in a conventional lamp. In the case of a luminous pressure of 1.9xc3x97106 Pa there is no foil floating, while at a luminous pressure of greater than 2.0xc3x97106 Pa the foil floating phenomenon occurs with high probability. This foil floating phenomenon is formed on the inside of the foil. The invention is further described below using several embodiments shown in the drawings.